1. Field of the Invention
The invention relates to a data storage device and, more particularly, to a device to store a large capacity of data such as image data of a number of picture planes or the like.
2. Related Background Art
A semiconductor memory of a large capacity has relatively cheaply been provided due to the improvement of the semiconductor technique and the use of such a memory as a recording medium of an image recording and reproducing apparatus or as a recording medium in the recording, reproducing, or editing process or the like has been proposed. As compared with the case of using a magnetic tape, magnetic disk, or the like as a recording medium, there are advantages such that the recorded images can be searched at a high speed, a moving image of an arbitrary synchronizing frequency can be recorded and reproduced, and the data can be easily copied or rearranged in the medium.
To store data such as images having a large information amount, however, a very large memory capacity is needed and it is difficult to manage addresses. Namely, in general, since the information amount per unit of the image (that is, per field or frame of the image) is not always equal to the power of 2, processes to allocate the address to each image becomes complicated. To simplify the address allocation, there is considered a method whereby the information amount per unit of the image is forcedly equalized to the power of 2 by adding dummy data or the like. However, the use of such a method causes a use efficiency to be deteriorated.
Therefore, the access to the image memory device has conventionally been performed on a pixel unit basis. A method of accessing to the image memory through an input/output bus has been proposed as a method of realizing multiports, namely, a plurality of inputs and outputs. Even in case of using such a method, however, the access is fundamentally executed on a pixel unit basis.
As mentioned above, even if multiports are realized, since there is a limitation of a transfer speed of the input/output bus, while one input/output (I/O) circuit is accessing, it is difficult to interrupt the access of another I/O circuit. Particularly, in case of the image memory device of a large capacity, the process is frequently waited for a long time.